Light-emitting diode is a semiconductor P-N junction diode; when a forward voltage is applied to both ends of a P-N junction, the current carriers are excited from low-energy state to high-energy state and are in an unstable state, and when the carriers return to low-energy state and recombination is to occur, according to the conservation of energy theorem, excessive energy is released in the form of photons. External quantum efficiency of light emitting diode is the key to improve the light emitting diode luminous efficiency, and depends on the internal quantum efficiency of epitaxial materials and the light extraction efficiency of epitaxial wafer. Now breakthroughs have been made in precise control of epitaxial growth, doping concentration and reduction of dislocations, and internal quantum efficiency of light emitting diode has been already very high, therefore, the light extraction efficiency of epitaxial wafer will determine the luminous efficiency of light emitting diode to a great extent.